1. Field of the Invention
The present invention relates to a system and method of generating a public long code mask (PLCM) in a mobile communications system.
2. Discussion of the Related Art
In the world of cellular telecommunications, those skilled in the art often use the terms 1G, 2G, and 3G. The terms refer to the generation of the cellular technology used. 1G refers to the first generation, 2G to the second generation, and 3G to the third generation.
1 G is used to refer to the analog phone system, known as an AMPS (Advanced Mobile Phone Service) phone systems. 2G is commonly used to refer to the digital cellular systems that are prevalent throughout the world, and include CDMAOne, Global System for Mobile communications (GSM), and Time Division Multiple Access (TDMA). 2G systems can support a greater number of users in a dense area than can 1G systems.
3G is commonly used to refer to the digital cellular systems currently being developed. Recently, third-generation (3G) CDMA communication systems have been proposed including proposals, such as cdma2000 and W-CDMA. These 3G communication systems are conceptually similar to each other with some significant differences.
A cdma2000 system is a third-generation (3G) wideband, spread spectrum radio interface system that uses the enhanced service potential of CDMA technology to facilitate data capabilities, such as Internet and intranet access, multimedia applications, high-speed business transactions, and telemetry. The focus of cdma2000, as is that of other third-generation systems, is on network economy and radio transmission design to overcome the limitations of a finite amount of radio spectrum availability.
Referring to FIG. 1, a subscriber uses a Mobile Station to access network services. The Mobile Station may be a portable communications unit, such as a hand-held cellular phone, a communication unit installed in a vehicle, or even a fixed-location communications unit.
The electromagnetic waves from the Mobile Station are transmitted by the Base Transceiver System (BTS) also known as node B. The BTS consists of radio devices such as antennas and equipment for transmitting radio waves. The Base Station Controller (BSC) receives the transmissions from one or more BTS's. The BSC provides control and management of the radio transmissions from each BTS by exchanging messages with the BTS and the Mobile Switching Center (MSC) or Internal IP Network. The BTS's and BSC may be part of the Base Station (BS).
FIG. 2 illustrates a data link protocol architecture layer for a wireless network. The upper layer contains three basis services; voice services 62, data services 61 and signaling 70. Voice services 62 include PSTN access, mobile-to-mobile voice services, and Internet telephony. Data services 61 are services that deliver any form of data on behalf of a mobile end user and include packet data applications (e.g., IP service), circuit data applications (e.g., asynchronous fax and B-ISDN emulation services), and SMS. Signaling 70 controls all aspects of mobile operation.
In the CDMA2000 communication system, a long code is used in forward channel for ciphering the forward channel and determining the location of a power control bit. In the reverse channel, the long code is used as an element for identifying each terminal and reducing interference among subscriber terminals.
A long code is, typically, constructed of 42 bits. FIG. 3 is a block diagram of a related art method for generating a long code and transmitting a transmission signal using the long code based on a long code mask. As shown, a long code (a long code sequence) is generated based on a 42-bit long code mask. The generated long code undergoes modulo-2 inner product of a transmission signal X.
The long code mask may be separately generated for each channel. The long code mask is used in common channels based on the above method. In traffic channels, the long code mask is generally referred to as a public long code mask or PLCM. When a voice signal is ciphered in the traffic channels, it is referred to as a private long code mask. A long code is used for scrambling and spreading as provided in further detail below.
A long code is a sequence used for scrambling on the Forward CDMA channel and spreading on the reverse CDMA channel. The long code uniquely identifies a mobile station on both the reverse traffic channel and the forward traffic channel. The long code provides limited privacy. The long code also separates multiple access channels and enhanced access channels on the same CDMA Channel. A long code mask is a 42-bit binary number that creates the unique identity of the long code, for example. A private long code is the long code characterized by the private long code mask. A private long code mask is the long code mask used to form the private long code. A public long code is the long code characterized by the PLCM. A PLCM is the long code mask used to form the public long code. The mask can contain a permutation of the mobile station's ESN, or the particular mask specified by the base station. The mask also includes the channel number information when used for supplemental code channel.
The PLCM used in the traffic channel is shown in FIG. 4 and FIG. 5. FIG. 4 is a diagram of a PLCM for a reverse fundamental channel, and a reverse supplemental code channel, wherein radio configuration (RC) is 1 or 2.
FIG. 5 is a diagram of a PLCM for a reverse fundamental channel, a reverse supplemental channel, a reverse dedicated control channel, a forward fundamental channel, a forward supplemental code channel, a forward supplemental channel, a forward dedicated control channel, or a forward packet data channel, wherein radio configuration (RC) is, for example, 3, 4, 5, and 6.
Referring to FIG. 4 and FIG. 5, the PLCM includes PLCM_37 (e.g., positions M36˜M0) constructed with least significant 37 bits. The PLCM_37 can be divided into first significant segment M36˜M32, and second significant segment M31˜M0. A code channel index i, as shown in FIG. 4, indicates three bits M39˜M37 in front of the first least significant bits M36˜M32. The value of ‘000’ for the code channel index i indicates a reverse fundamental channel. Values ‘001’ to ‘111’ indicate a reverse supplemental code channel, where i=1˜7, for example.
A base station can inform a mobile terminal how the least significant 37 bits PLCM_37, (i.e., the first least significant 5 bits M36˜M32 and the second least significant 32 bits M31˜M0), of the PLCM are generated via an extended channel assignment message (ECAM).
FIG. 6 is a diagram of a method of generating the least significant 37 bits PLCM_37 of the PLCM according to a PLCM type PLCM_TYPE defined in the ECAM.
The PLCM_TYPE is 4 bits. If the PLCM_TYPE is received from the base station through the ECAM is ‘0000’, the terminal sets the first least significant 5 bits (M36˜M32) to ‘11000’ and sets the second least significant 32 bits (M31˜M0) by using the following equations 1 and 2 to calculate a permutated ESN.ESN={E31, E30, E29, . . . , E2, E1, E0}  [Equation (1)]M31˜M0={E0, E31, E22, E13, E4, E26, E17, E8, E30, E21, E12, E3, E25, E16, E7, E29, E20, E11, E2, E24, E15, E6, E28, E19, E10, E1, E23, E14, E5, E27, E18, E9}  [Equation (2)]
The ESN is an identifier assigned to the terminal in the communication system, and is used for call processing. It may be needed that the least significant 37 bits (M36˜M0) of the PLCM be changed during hand-off or when the mobile terminal is communicating with the base station. As such, the present invention is needed in two scenarios. First, during handoff and second when the method of generating PLCM needs to be changed when base station and mobile terminal are in communication.
In some cases, the terminal generates the least significant 37 bits (M36˜M0) using the PLCM_TYPE and the least significant 32 bits PLCM_32 provided by the base station. Later, when the mobile terminal moves to a new cell, the base station in the new cell may require the mobile terminal to generate the least significant 37 bits (M36˜M0) of the PLCM using the ESN
While the above method is supported in the related art handover systems and methods, the reverse is not. That is, a new cell may require the mobile terminal to use a long code mask generated based on a value (PLCM_32) provided by the base station, when the old cell required the mobile terminal to use the ESN.
Unfortunately, the current systems and methods do not support a transition from a base station supporting the ESN based long code mask to a base station supporting a base station assigned long code mask scheme. Particularly, a problem arises when a base station assigned long code mask scheme is used by a mobile station when the mobile station enters a communication network where a base station assigned long code mask scheme should not be used. A method and system is needed to overcome the mentioned problem.